Electrode for photovoltaic cells, photovoltaic cell and photovoltaic module

ABSTRACT

An electrode is described for contacting an electrically conductive surface, in particular for contacting at least one surface of a photovoltaic element wafer  3 , the electrode comprising an electrically insulating optically transparent film  10 , an adhesive layer  11  provided on one surface of said film  10 , and a first plurality of substantially parallel, electrically conductive wires  5′  being embedded into the adhesive layer  11,  a part of the surfaces of said wires  5′  protruding from the adhesive layer  11  and at least on the surface protruding from the adhesive layer  11  being covered by a coating  2  consisting of an alloy with a low melting point, wherein the wires  5′  of the first plurality are electrically connected to a first terminal bar  20 . A plurality of said electrodes may be formed as an endless, continuous strip, which can be cut to a length corresponding to that of an array of adjacent photovoltaic elements  3  to be connected for forming a PV module, wherein the wires  5′  running in longitudinal direction of the strip are cut at distances corresponding to the distances of the PV cells. A PV cell or a PV module comprising at least one electrode  16  or one electrode strip  16  as described above may comprise one or more photovoltaic cells  3  with an electrically conductive, antireflective, optically transparent coating  4  on at least one of its surfaces, the wires  5′  of the first plurality being soldered onto the coating  4  and onto the respective terminal bars  20  or terminal frames  17  by means of the alloy  2.

The invention relates to an electrode for contacting electricallyconductive surfaces, in particular for contacting one or a plurality ofphotovoltaic (PV) elements being part of a photovoltaic cell or solarcell. The invention further relates to photovoltaic cells produced withthis electrode.

The generation of electrical energy using photovoltaic technology hasreached a high standard. However, the production of PV cells and PVmodules is still rather complicated and expensive. Also the efficiencyof energy generation using PV modules with a maximum efficiency of about17 percent is rather low. From an economic point of view the generationof electric power using photovoltaic technology is only acceptable undercurrent conditions if it is supported and/or subsidized by some means,e.g. by the so called 100 000-roofs program in Germany or similarprograms in California, USA. Thus, in the field of photovoltaictechnology there still remains a critical requirement to lower theproduction costs and enhance the efficiency of the energy generationusing PV elements and PV modules.

Commonly used PV cells comprise a semiconductor element with a junctionof the type (n⁺n (or p) p⁺) on the basis of mono- or multicrystallinesilicon, amorphous silicon and other thin-film semiconductors with anembedded p-n junction. One surface of the element is usually coveredwith a metal layer, such as aluminum or stainless steel, while the othersurface is provided with an anti-reflective coating. Both surfaces arein contact with electrodes, which collect and carry off the generatedelectrical energy. This structure is embedded between transparentprotective layers, such as glass.

The electrodes are all produced using screen-printing technology.However, electrodes produced this way have a high series resistance.Apart from this, expensive devices and equipment are required for theproduction and cost reduction is limited when this technology isemployed.

From the patent U.S. Pat. No. 5,759,291 A (Inchinose et. al.) asemiconductor element (wafer) with parallel metallic contact or currentcollecting wires (electrodes) which are fixed to the surface of theelement by means of a conductive adhesive, in which conductive particlesare dispersed is known. These electrode wires are arranged in parallelbetween connecting conductors which are running along the edges of theelement. For this type of electrode the ohmic contact resistance betweenthe semiconductor surface and the wires is relatively high, whichresults in a high energy loss and a low efficiency especially underconcentrated solar radiation. Also, the production of such PV cells israther complicated.

From the patent U.S. Pat. No. 5,084,107 A (Deguchi et. al.) a similarsolar cell and array of solar cells are known, wherein metallicelectrode wires are adhered to the surface of the photovoltaic elementby means of an adhesive material. In the adhesive, conductive particlesare dispersed. Also with this electrode structure, the production costsand the contact resistance between the wires and the surface of theelement are fairly high.

From the patent U.S. Pat. No. 5,158,618 A (Rubin et al.) an electrodestructure is known, wherein the contact wires are embedded in atransparent polymer block in such a way, that they partly protrude fromthe polymer block. Said electrodes contact the element from one or fromtwo sides and are sandwiched between transparent protective layers, suchas glass. As the wires of the electrode are, for example, configured ascoils, there are only point contacts between the wires and the surfaceof the PV element. Thus, also in this case the series resistance of a PVcell is relatively high. Also the production costs are relatively high,since the automated production of such types of solar cells and PVmodules is not possible.

An objective of the invention is therefore to provide for an electrodewhich at low production costs achieves a lower contact resistancebetween the electrodes and a conductive surface, in particular thesurface or surfaces of a photovoltaic element.

A further objective of the invention is to provide for a PV cell whichallows, by using such an electrode, lowering the combined seriesresistance and the production costs of PV cells and PV modules andenhancement of their efficiency.

The invention achieves these objectives by providing an electrode forcontacting an electrically conductive surface, in particular forcontacting at least one surface of a photovoltaic element, the electrodecomprising an electrically insulating optically transparent film, anadhesive layer provided on one surface of said film, and a firstplurality of substantially parallel, electrically conductive wires beingembedded into the adhesive layer, a part of the surfaces of said wiresprotruding from the adhesive layer and at least on the surfaceprotruding from the adhesive layer being covered by a coating consistingof an alloy with a low melting point, wherein the wires of the firstplurality are electrically connected to a first terminal bar.

Preferably, a second plurality of wires substantially running parallelto each other is disposed between the transparent film and the wires ofsaid first plurality, the wires of the first and second pluralitiesforming together a mesh, and the wires of the second plurality beingelectrically connected to a second terminal bar.

In a further preferred embodiment the first and second terminal bars areelectrically connected to each other.

The terminal bar(s) may be provided at the respective ends of the wires.

In that embodiment the terminal bar(s) are preferably provided atopposite ends of the wires of the first or of the first and secondpluralities of wires outside the contour of the photovoltaic element, tothe surface of which the wires are to be connected.

The first and second terminal bars are preferably connected to form anangle.

In a further preferred embodiment the terminal bars are formed as aU-formed frame, the wires of one of the two pluralities being connectedto the base and the wires of the other plurality being connected to thefree legs of the U.

In the embodiment when the terminal bar(s) are provided at opposite endsof the wires of the first or of the first and second pluralities theterminal bars are preferably extending over the length of two adjacentphotovoltaic elements to be connected and that a step is provided intheir centre, so that a plurality of terminal bars can be fit togetherforming one row, in which the one half of a terminal bar is arrangedbelow or above the lower or upper halves, respectively, of theneighbouring terminal bar, wherein between the terminal bars aninsulating film is provided.

Further, the terminal bars may be formed as a closed frame, the openarea (window) of said frame exceeding the dimensions of thecorresponding photovoltaic element.

It is a further preferred embodiment to have the terminal bar(s) formedas a double frame with two adjacent windows, the open area of whichexceeds the dimensions of the corresponding photovoltaic elements.

The frame may comprise two metallic frames with an insulating filmprovided between them.

In a further preferred embodiment a step is provided in the central barof the double frame, so that a plurality of frames can be fit togetherforming one row, in which the one half of a double flame is arrangedbelow or above the lower or upper halves, respectively, of theneighbouring double frame.

A slot can be provided in the central bar of the double frame, and saidslot running parallel to said step, so that upon completion of a PVmodule the traversing wires of the electrode can be cut.

Finally, metallic bars may be arranged spanning over at least one windowof the frame(s), said bars being integrally connected with thecorresponding metallic frame.

The invention further achieves the above objectives by providing aplurality of electrodes according to any of the embodiments describedabove wherein the electrodes are formed as an endless, continuous strip,which can be cut to a length corresponding to the length of an array ofadjacent photovoltaic elements to be connected for forming a PV module,wherein the wires running in longitudinal direction of the strip are cutat distances corresponding to the distances of the PV cells.

Preferably, an endless terminal bar may be provided along at least oneof the edges of the transparent film wherin, again preferably, alongeach edge of the transparent film there are arranged comb-like terminalbars, the teeth of which reaching respectively from one side between twoadjacent photovoltaic elements over the width of the wires of the firstplurality and alternately being in electrical contact with the upper andlower sides of corresponding photovoltaic elements and being isolatedfrom the other surface.

The invention farther achieves the above objectives by providing a PVcell or a PV module comprising at least one electrode or one electrodestrip according to any of the preceding embodiments, comprising one ormore photovoltaic cells with an electrically conductive, antireflective,optically transparent coating on at least one of its surfaces, the wiresof the first plurality being soldered onto the coating and onto therespective terminal bars or terminal frames by means of the alloy.

When the wires of the first and second pluralities are arranged to forma mesh the wires of the first and second pluralities are preferablybonded together at their crossing points and onto the respectiveterminal bars or terminal frames by means of the alloy.

The electrode according to the invention provides for an intimate andreliable ohmic contact with the surface to be contacted and providesachievement of 8 to 10 times lower combined series resistance of a PVcell or PV module which not only improves the PV elements' efficiencybut allows them to operate under 8 to 10 times concentrated solarradiation. This refers particularly to those embodiments, wherein thewires of the first and second pluralities are arranged with respect toeach other in the form of a mesh and are connected to angularly orrectangularly formed connecting conductors. Simultaneously, duringproduction the degree of automation and the throughput capacity may besubstantially increased.

In the following, the invention is explained in more detail by theembodiments illustrated in the drawings.

FIG. 1 is a schematic isometric partial view of a PV cell before, and

FIG. 2 after a heating and/or pressing step during the production of aPV cell,

FIG. 3 is a schematic isometric view of a mesh of contact wires,

FIG. 4 is a schematic isometric view of a device for producing film-typeadhesive optically transparent electrodes,

FIG. 5A is a view of an electrode produced with the device of FIG. 4,

FIG. 5B shows the cross-section A-A of FIG. 5A,

FIG. 5C is a view of an electrode strip with wires running transverselyto the direction of the wires of FIG. 5A,

FIG. 5D shows the cross-section A-A of FIG. 5C,

FIG. 6A shows the view of an electrode strip with a wire mesh,

FIG. 6B shows the cross-section B-B of FIG. 6A,

FIG. 6C shows the cross-section A-A of FIG. 6A,

FIG. 7 shows in a schematic isometric exploded view the essentialelements of a PV cell before heating and pressing,

FIG. 8 is a schematic isometric exploded view of a second embodiment ofthe elements of a PV cell before heating and pressing.

FIG. 9A is a view of a third embodiment of a PV cell,

FIG. 9B shows the cross-section A-A of the photovoltaic element of FIG.9A,

FIG. 10A is the view of several PV cells being arranged in the form of astrip, which PV cells are connected to each other in parallel,

FIG. 10B shows the section A-A of FIG. 10A,

FIG. 10C shows the section B-B of FIG. 10A,

FIG. 11A is the view of several PV cells in the form of a strip and withelectrodes forming a mesh, which cells are connected to each other inparallel,

FIG. 11B shows the section A-A of FIG. 11A,

FIG. 12A shows a further embodiment of an array of PV cells beingarranged in the form of a strip in which PV cells are connected inseries,

FIG. 12B shows the section A-A of FIG. 13A,

FIG. 13 is the view of a further embodiment of an electrode strip withelectrode wires arranged in the form of a mesh, wherein the PV cells arealso connected to each other in series,

FIG. 14A is the view of an endless electrode with single electrodesections for forming one PV cell, respectively.

FIG. 14B shows the section A-A of FIG. 12A,

FIG. 15A is the view of an array of PV cells being arranged in series inthe form of a strip,

FIG. 15B shows the section A-A of FIG. 15A,

FIG. 15C shows the section B-B of FIG. 15A,

FIG. 16A shows a further embodiment of several PV cells being arrangedin series in the form of a strip,

FIG. 16B shows the section A-A of FIG. 16A,

FIG. 16C shows the section B-B of FIG. 16A,

FIG. 17 is a schematic exploded view of the elements of a PV module withseries-connected PV cells,

FIG. 18 shows a further embodiment of a PV module similar to that ofFIG. 17, and

FIG. 19 shows a further embodiment of a PV module similar to that ofFIGS. 17 and 18.

FIG. 1 shows a semiconductor structure S, for example Silicon (n⁺n (orp) p⁺), the upper surface of which (always in relation to the depictionin the figure) is covered with an anti-reflective, transparent,electrically conductive coating 4 such as, for example, Indium-Tin-Oxide(ITO). The element S can also consist of a thin-film PV element. Thelower surface of the element S is coated either with a metal coating(e.g. aluminium) or alternatively with an anti-reflective, transparent,electrically conductive coating 4. The element S and the upper coating 4form together with the metal coating (not depicted) or the second, lowerITO-coating 4 a unit, hereinafter referred to as a wafer 3. The twosurfaces of the wafer 3 are in contact with the metallic wires 1, whichare coated with a coating 2 consisting of an alloy having a low meltingpoint. The wires 1 may be completely coated with the alloy coating 2 oronly partly coated on the side or sides facing the surface to becontacted In the following, the coated wires are referred to as a firstplurality of wires 5′. They are in direct contact with the surface orsurfaces of the wafer 3.

FIG. 2 shows the arrangement of FIG. 1 after pressing and heating up to120°. The material of the alloy coating 2 has slightly softened andwetted the coating 4, and is in ohmic contact with said coating and thewires 5′. The same refers to the case in which the lower side of theelement S is not to be provided with an anti-reflective, transparent,conductive coating 4, but with a metal coating. The distance of thewires 5′ is not required to be uniform, i.e. the parallel wires 5′ maybe arranged in pluralities of two or more wires 5′ with differentdistances between the wires and the wires of a plurality.

The cross-sectional form and size of the wires are chosen to optimisethe electric current collection by the wires, the current density in thewires, the series resistance of the PV cell and the size of the waferarea shadowed by the wires 5′. As shown in FIGS. 1 and 2, differentcross-sectional forms may be chosen for the wires 5′, for examplecircular, rectangular, triangular etc. Of course, for the wires 5′ of aparticular PV cell or PV module respectively only one cross-sectionalform is chosen.

FIG. 3 shows a wire mesh 6 of wires 5′ of the first and wires 5″ of asecond plurality, wherein the wires 5′, 5″ of the first and secondpluralities are usually running perpendicularly to each other. The wires5″ are, at least on the surfaces facing the wires 5′, also covered withan alloy coating 2. However, if the amount of alloy material on thewires 5′ of the first plurality is sufficient for a safe mechanical andelectrical connection of the two pluralities of wires at the crossingpoints, the alloy coating on the wires 5″ of the second plurality couldbe omitted. As to the choice of the distances of the wires 5″ and of thecross-sectional form and area, the same considerations as for thearrangement and size of the wires 5′ are to be applied. Of course, forthe wires 5″ a cross-sectional form and size different from that of thewires 5′ can be chosen.

FIG. 4 shows the schematic view of a device for producing a film-typeadhesive optically transparent electrode. Initially, the alloy-coatedwires 5′ are wound up on several rolls 7, the number of which equals thewidth of the PV cell divided by the required distances between theparallel running wires 5′ of the first plurality. For example, at awidth of the PV cell of 100 mm and a distance between the wires of 4 mm,26 rolls 7 are required. The rolls 7 are fastened on an axis 8, so thatit is possible to form parallel lines of wires 5′, which are runningthrough corresponding openings in a frame 9. The distance between theopenings in the frame 9 is determined by the requested distance betweenthe parallel wires 5′. Size and form of the openings in the film 9 haveto correspond to the size and form of the cross-sectional area of thewires 5′.

The parallel wires 5′ are disposed on a polymeric film 10, which issupplied from a drum 12. The surface of the film 10 facing the wires 5′is coated with a transparent adhesive 11. The overall width of the film10, on which the wires 5′ are placed, exceeds the width of one or anarray of several wafers 3, so that on each side of the film 10 a zone of1.5 to 2 cm remains free of wires 5′ (FIG. 5A). The film 10 is lead bythe drum 12 over the surface of a rotatable roller 13 and is pulled by adrum 15, simultaneously pulling the wires 5′. The wires 5′ are pressedon the film 10 by means of another roller 14 arranged above therotatable roller 13. Simultaneously, the film 10 is heated by therollers 13 and 14, so that the adhesive 11 softens, the wires 5′ immersein the adhesive 11 and, after cooling down, remain fixed to the film 10and embedded in the adhesive 11. It is recommended that the oppositeside of the polymeric film should be primed by adhesive material toallow further PV cell encapsulation between protective layers.

FIGS. 5A and 5B show in detail the result of this process, namely atransparent electrode 16. The wires 5′ extending along the polymericfilm 10 are embedded in the adhesive 11 and pressed onto the film 10. Apart of the surface of the wires 5′ is protruding from the surface ofthe adhesive 11. In FIG. 5B, on the left and right-hand other possiblecross-sectional forms of the wires 5′ are again depicted.

A production device similar to that of FIG. 4 may be used for producinga polymeric film 10 with embedded wires 5′ being transversely arrangedto the initial direction of the film 10 (FIGS. 5C, 5D). The width of thepolymeric film 10 has hereby to correspond to the required length of aPV cell or PV module. After the wires 5′ of the first plurality areembedded in the film 10, it may be cut in pieces transverse to theinitial extension of the film 10.

The distance of the wires 5′ and/or 5″ is not required to be uniform,i.e. the parallel wires 5′ and/or 5″ can be arranged in groups of two ormore wires with different distances between the wires in each group andnumber of such groups.

FIG. 6A shows an electrode 16 comprising the transparent polymeric film10 and a wire mesh 6 of the wires 5′ and 5″ of the first and secondpluralities. Only the wires 5″ being more closely located to thepolymeric film 10 are immersed in the adhesive 11 (see also FIGS. 6B and6C). The upper wires 5′ coming into contact with the surface or surfacesof the wafer 3 are not, at least not completely, immersed in theadhesive 11 (during the production of this type of an electrode 16 theroll 7 carries a wire mesh 6, and fine 9 is not used (FIG. 4)). Alreadyat this point, the wires 5′, 5″ may be soldered together. However,usually this is done at the time of assembly of the electrode 16 and thewafer 3.

For the polymeric film 10 a wide range of materials may be used: thematerial must have a high ductility, good insulating characteristics,optical transparency and thermal stability, resistance to shrinkage andhave a good adhesive ability. Examples of such materials arecellophane®, rayon, acetate, fluororesin, polysulfone, epoxy resin, andpolyamide resin. A suitable material to be used is also the transparentpolymeric film Mylar®. Materials to be preferably used are those basedon a fluoropolymer, for example the polyvinyl fluoride film Tedlar® andthe modified ETFE fluoropolymer resin Tefzel®. These materials are usednot only in photovoltaic industry but also for general purposes and forelectrotechnical products for lamination purposes.

A wide range of materials having a softening temperature ranging fromabout 90-110° C. and having a good adhesion to preliminarily primedpolymeric films and the surface of the wafer 3 are suitable as adhesive11. Preferred materials are acrylic adhesive materials rubber adhesiveis, silicon adhesive materials and polyvinyl ether adhesive materials aswell as epoxy adhesive materials. Materials to be most preferably usedare Ethylene Vinyl Acetate, for example, supplied by HI-SHEETINDUSTRIES, LTD and those supplied by Dupont: 68080 Polymethylmethacrylate, 68040 Methacrylate copolymer, 68070 Methacrylatecopolymer.

The adhesive layer 11 has to be sufficiently thick in order to providefor a reliable connection of the electrode with the wafer 3. Thethickness of the adhesive layer should, however, not exceed thethickness of the wires 5, so that the part of the wires 5′ protrudingfrom the adhesive 11, which part is coated with the alloy 2 and is notimmersed in the adhesive 11 can later on form a direct ohmic contactwith the electrically conductive surface of the wafer 3 (FIGS. 5A, 5D,6B, 6C).

The polymeric film 10 has to be sufficiently thick, so that it issufficiently stable when the adhesive 11 is applied and when it ispulled under pressure and heat when attaching the wires 5, 5″.Simultaneously, it should be as thin as possible in order to achievehigh elasticity and transparency for the light passing through it.Preferably, the thickness of the polymeric film 11 ranges between 10 and50 μm. As was mentioned before it is preferable if the opposite side ofpolymeric film is primed with adhesive material.

In FIGS. 5 and 6 the polymeric film 10 is shown with the adhesive 11 andthe wires 5′ (or the mesh 6 with the wires 5′, 5″) with the alloycoating 2 protruding from the surface of the adhesive 11, forming acontinuous or endless film-type optically transparent adhesive electrode16.

The electrode 16 of this invention may be applied for the production ofPV cells and PV modules Hereby, different types of metallic rods or barsand connections are E d in order to collect the current from theelectrode 16 and transmit it further. It is hereby advisable to attachthe metallic rods or bars to the electrode 16 by some drops of glue orby brief local beating, thus bonding or fixing the metallic rods or barsto the adhesive 11 of the electrode 16. The distance between themetallic bars and different types of connections has to be designed insuch a way that there is enough space between the wafers 3 so that theywill not come into direct electrical contact with the constructionalelements when they thermally expand under up to 160° C. heating duringthe assembly of the wafer 3 and the electrode 16.

FIG. 7 shows a drawn out depiction of a PV cell before its assembling bymeans of pressing and heating. Electrodes 16 are res vely disposed aboveand below the wafer 3. In a direction transverse to the longitudinalextension of the wires 5′ of the electrodes 16, there are disposed attwo opposite sides of the wafer 3 a first terminal bar 20 and a secondterminal bar 22, which on their lower or upper sides, respectively, areprovided with a coating 21 consisting of an electrically conductivealloy with a low melting point. The wires 5′ of the upper electrode 16are extending from the right border of the wafer 3 up to the left edgeof the second terminal bar 22. In reverse, the wires 5′ of the lowerelectrode 16 are extending from the left edge of the wafer 3 to theright edge of the first terminal bar 20. After heating and pressing, thewires 5′ of the upper electrode 16 are in ohmic contact with the left,second terminal bar 22 and the upper surface of the wafer 3, while thewires 5′ of the lower electrode 16 are in ohmic contact with the lowerside of the terminal bar 20 and the lower side of the wafer 3.

The electrically conductive alloys 2, 21 with a low melting point may berepresented either by common solders or specially developed ones on thebasis of different metals, like Ag, Bi, Cd, Ga, In, Pb, Sn, Ti, etc. Itis also possible to use electroconductive material composed of organicadhesives with metallic or alloy particles.

FIG. 8 shows a similar structure, however with angularly formed terminalbars 20, 22 and electrodes 16 with wires 5′, 5″ arranged in the form ofa mesh 6. After pressing and heating, the mesh 6 of the lower electrode16 is in ohmic contact with the right, first angularly formed terminalbar 20 and the lower side of the wafer 3, while the mesh 6 of the upperelectrode 16 is in ohmic contact with the second angularly formedterminal bar 22 and the upper side of the wafer 3.

FIGS. 9A and 9B show a PV cell, wherein the terminal bars are configuredin the form of a three-layered laminated frame 17, in the window ofwhich the corresponding wafer 3 is accommodated. The wires 5′ arerunning between two opposite sides of the frame 17, onto which sidesthey are soldered as a result of heating and pressing.

As shown in more detail in FIG. 9B, the frame 17 comprises two metallicframes 18, between which there is disposed a preferably double-sidedadhesive insulating film 19. On the outer sides of the two frames 18,respectively, a conductive alloy coating 21 is applied This coating maybe omitted when the amount of the material on the wires 5′ is sufficientfor a reliable ohmic contact between the frame 17 and the wires 5′. Inthis case it is recommended that the frame 17 should be tinned.

This embodiment is also suitable for use with an electrode 16 in theform of a mesh, wherein the wires 5″ of the second plurality (not shown)are running perpendicularly to the wires 5′ of the first plurality andare in ohmic contact with the corresponding sides of the frame 17depicted in FIG. 9.

The following embodiments illustrate how, with the help of the electrode16 of this invention, which is produced in the form of an endless strip,an array of PV cells may be connected in series and parallel to eachother thereby constituting PV modules.

FIGS. 10A, 10B and 10C show an endless electrode 16 with comb-liketerminal bars 23, the longitudinal bars 24 of which outside the wires 5′are running in parallel to them in the direction of the longitudinalextension of the endless electrode 16. The longitudinal bars 24 areintegrally connected with transversely running transverse bars 25 (the“teeth” of the comb), which from the one or the other direction,respectively, are protruding into the spaces between the wafers 3.

As shown in FIG. 10B (cross section A-A of FIG. 10A), the upper surfacesof the left transverse bars 25 are provided with an insulating film 19,while on the lower surface a coating 21 is applied consisting of anelectrically conductive alloy. For the right transverse bars 25 theinsulating film 19 is deposited on the lower surface and the coating 21consisting of a conductive alloy is deposited on the upper surface.

FIG. 10C shows the cross section B-B of FIG. 10A.

In the embodiment shown in FIGS. 10A to 10C the PV cells arranged thatway are connected in parallel with each other, since the reeve lefttransverse bars 25 are electrically connected to the lower sides of thewafers 3 and the respective right transverse bars 25 are electricallyconnected with the upper side of the wafers 3 being located on the rightside of them.

FIGS. 11A and 11B show an embodiment, wherein the PV cells parallelconnections similar to FIGS. 9A and 9B are configured in the form of athree-layered frame 17, which is laminated from an endless array ofmetallic frames 18 arranged in series and an insulating polymeric film19 arranged between these frames 18. On the outer sides of the frames 18a conductive coating 21 melting at low temperatures is deposited. Thiscoating 21 is in ohmic contact with the wires 5′ and 5″ of the electrode16.

In this embodiment the wafers 3 are positioned within the “windows” offame 17 and the PV cells are connected in parallel to each other bymeans of the upper and lower electrodes 16.

FIGS. 12 A and 12 B show a series connection of several PV cells. Theterminal bars 25 running in transverse direction to the longitudinalextension of the electrode 16, with periodically interrupted wires 5,are provided with a coating 21 on their upper and lower sides,respectively. Hereby, the wires 5′ of the upper electrode 16 provideohmic contact between the upper side of a terminal bar 25 and the upperside of the wafer 3 arranged on the right side thereof, whereas thewires 5′ of the lower electrode 16 provide ohmic contact between thelower side of each terminal bar 25 and the lower side of the wafer 3arranged on the left side thereof.

FIG. 13 shows an endless electrode 16, wherein the PV cells' seriesconnection is accomplished by means of U-formed metallic terminal bars26. Bars 24 of the terminal bars running in the longitudinal directionare in ohmic contact with the wires 5″, and the transverse bars 25thereof running in a transverse direction to the electrode 16 are inohmic contact with the wires 5′. The wafers 3 are positioned within thespace of the U-formed metallic terminal bars 26 and between the upperand lower electrodes 16.

The connections of the wafers 3 with wires 5′ are similar to that shownin FIG. 12B.

FIGS. 14A and 14B show an electrode 16 as it may be used for the PVcells' series connection as depicted on FIGS. 12A and 12B andanalogously for the arrangement of FIG. 13. The wires 5′ are eachinterrupted by perforations 29, which include either only one wire 5′ orseveral wires 5′, respectively. Of course, the solidity of the electrode16 remains better when the perforations 29 interrupt only one wire 5′,compared with the case where several neighbouring wires are perforated.In the latter case it is recommended that a strip of transparentadhesive polymeric film (not shown) be applied on the perforated part ofthe electrode 16 in a direction transverse to the longitudinal extensionof the electrode 16.

Similarly, in the embodiment of FIG. 13 the terminal bars 24 running inthe longitudinal direction may also be interrupted, along with the wires5′. Thus, on the lower and upper side of wafer 3 respectively there maybe used identical electrodes 16, which are shifted with respect to eachother only by the width of the distance between the transverse bars 25and the edge of the next wafer 3.

A basically different construction of the connections for caking off theelectrical energy is described with reference to FIGS. 15 to 19.

The basic element of the arrangement according to FIG. 15 is a laminatedthree-layered double frame 27 comprising two metallic frames (preferablycopper foil) 28 and an insulating film 19 provided between these frames.In the central bar of double frame 27 and parallel thereto a step isprovided. The height of said step corresponds to the thickness of themetal foil i.e. to about 0.2 to 0.3 mm (FIGS. 15A, 15B, 15C). As seenfrom FIG. 15B, the metallic frames 28 are superposed in positionsshifted with respect to each other, i.e. the left upper part of ametallic frame 28 is arranged above the right lower part of the leftadjacent frame 28. The insulating film 19 provided between the twosuperposing metallic frames 28 of adjacent double frames 27 is bent atits ends in an upward or downward direction and extends up to thesurface of the frame 27 construction. The wafers 3 are positioned withinthe “windows” of frame 27. The wires 5′ of the upper and lowerperforated electrodes 16 are in ohmic contact with the surfaces of thewafer 3, and the respective left and right bars of each of the framewindows. The wires 5″ are electrically connected with the wires 5′ andthe respective upper and lower bars of the frames. The surfaces of themetallic frames 28 in contact with the wires 5′ are, if necessary,coated with an alloy coating 21 having a low melting point or are justtinned.

Thus, it is possible to serially interconnect an array of PV cells ofany number.

FIGS. 16A, 16B and 16C show a similar, but substantially simplified,construction wherein the non-perforated electrode 16 corresponds to thatshown in FIGS. 5C and 5D. In this case longitudinal bars 32 with a stepare utilized. These longitudinal bars 32 are lined up like the frames 28as depicted on FIGS. 15B and 15C.

FIG. 17 shows in a drawn out depiction, representative of a whole array,two superposed metallic frames 28 with a step in the middle and arrangedin positions shifted with respect to each other. The special feature ofthis arrangement is that the transverse bars 31 are spanning over therespective right lower windows, said bars 31 being integrally connectedwith the metalic frame 28. In this embodiment, the bars 31 take over thefunction of the wires 5′ of the lower electrode 16 of this invention,i.e. in the completed PV cell they are in ohmic contact with therespective lower surface of the wafer 3 located above them.

In order to complete the endless array of series-connected PV cells,simple frames 30 are provided at their ends, wherein the simple frame 30provided for at the left end of the array is also provided with bars 31.

The construction is completed by an upper electrode 16 with electrodemeshes 6, the wires 5′ of which are perforated and after heating andpressing are connected with the upper surface of the wafer 3 and frames28 and 30. The lower electrode 16 has perforated wire 5″ sections orwire 5″ fields in longitudinal direction, said wire sections or wirefields being connected in the completed PV cell with the bars 31 and theframe 30. Here they take over the function of the wires 5″, i.e. of thewires being only indirectly connected with the lower surface of wafer 3.

FIG. 18 shows an embodiment similar to that of FIG. 17 with thedifference that instead of the lower electrode 16 a transparentpolymeric film 10 is provided to which an adhesive 11 is applied.

Finally, in FIG. 19 an embodiment is shown similar to that depicted inFIGS. 17 and 18. The upper electrode 16 has an uninterrupted mesh 6. Inorder that the wires 5′ of the electrode 6 can be perforated after thecompletion of series connection of the PV cells in the left bar and inthe central bar of the frame 28 as well as in the left and right bars ofthe upper and lower fame 30 a slot 33 is provided. This slot 33 runsparallel to the step. These slots 33 allow for the wires 5′ of the upperelectrode 16 to be cut throughout after assembly of the PV module. Thewidth of the slot 33 is calculated in such a way that the wires 5′ afterperforation remain permanently interrupted and isolated from each other.

1. An electrode for contacting an electrically conductive surface, inparticular for contacting at least one surface of a photovoltaic element(wafer 3), the electrode comprising an electrically insulating opticallytransparent film (10), an adhesive layer (11) provided on one surface ofsaid film (10), and a first plurality of substantially parallel,electrically conductive wires (5′) being embedded into the adhesivelayer (11), a part of the surfaces of said wires (5′) protruding fromthe adhesive layer (11) and at least on the surface protruding from theadhesive layer (11) being covered by a coating (2) consisting of analloy with a low melting point, wherein the wires (5) of the firstplurality are electrically connected to a first terminal bar (20). 2.Electrode according to claim 1, wherein a second plurality of wires (5″)substantially running parallel to each other is disposed between thetransparent film (10) and the wires (5) of said first plurality, thewires (5′, 5″) of the first and second pluralities forming together amesh (6), and the wires (5′) of the second plurality being electricallyconnected to a second terminal bar (22).
 3. Electrode according to claim2, wherein the first and second terminal bars (20, 22) are electricallyconnected to each other.
 4. Electrode according to any of the precedingclaims, wherein the terminal bar(s) (20, 22) are provided at therespective ends of the wires (5′, 5″).
 5. Electrode according to claim4, wherein the terminal bar(s) (20, 22) are provided at opposite ends ofthe wires of the first or of the first and second pluralities of wires(5, 5″) outside the contour of the photovoltaic element (wafer 3), tothe surface of which the wires (5′, 5″) are to be connected. 6.Electrode according to any of claims 1 to 5, wherein the first andsecond terminal bars (20, 22) are connected to form an angle (FIG. 8).7. Electrode according to any of claims 1 to 5, wherein the teal bars(20, 22) are formed as a U-formed frame, the mares of one of the twopluralities (5′) being connected to the base and the wires of the otherplurality (5″) being connected to the free legs of the U (FIG. 13). 8.Electrode according to claim 5, characterized in that the terminal bars(32) are extending over the length of two adjacent photovoltaic elements(3) to be connected and that a step is provided in their centre, so thata plurality of terminal bars (32) can be fit together forming one row,in which the one half of a terminal bar (32) is arranged below or abovethe lower or upper halves, respectively, of the neighbouring terminalbar (32), wherein between the terminal bars (32) an insulating film (19)(FIG. 16) is provided.
 9. Electrode according to claim 5, wherein theterminal bars are formed as a closed frame (17), the open area (window)of said frame (17) exceeding the dimensions of the correspondingphotovoltaic element (3) (FIG. 9).
 10. Electrode according to claim 5,wherein the terminal bar(s) is (are) formed as a double frame (17) withtwo adjacent windows, the open area of which exceeds the dimensions ofthe corresponding photovoltaic elements (3).
 11. Electrode according toclams 9 or 10, wherein the frame (17) comprises two metallic frames (18)with an insulating film (19) provided between them.
 12. Electrodeaccording to claim 10 or 11, wherein a step is provided in the centralbar of the double frame (17), so that a plurality of frames (17) can befit together forming one row, in which the one half of a double frame(17) is arranged below or above the lower or upper halves, respectively,of the neighbouring double frame (17).
 13. Electrode according to claim11 or 12, wherein a slot (33) is provided in the central bar of thedouble frame (28), said slot running parallel to said step, so that uponcompletion of a PV module the traversing wires (5′) of the electrode(16) can be cut.
 14. Electrode according to any of claims 9 to 13,wherein metallic bars (31) are spanning over at least one window of theframe(s), said bars (31) being integrally connected with thecorresponding metallic frame (18).
 15. A plurality of electrodesaccording to any of the preceding claims, wherein the electrodes areformed as an endless, continuous strip, which can be cut to a lengthcorresponding to the length of an array of adjacent photovoltaicelements (3) to be connected for forming a PV module, wherein the wires5′ running in longitudinal direction of the strip are cut at distancescorresponding to the distances of the PV cells (FIG. 14).
 16. Electrodestrip according to claim 15, wherein an endless terminal bar (22) isprovided along at least one of the edges of the transparent film (10).17. Electrode strip according to claim 16, wherein along each edge ofthe transparent film (10) are arranged comb-like terminal bars (23), theteeth (25) of which reaching respectively from one side between twoadjacent photovoltaic elements (3) over the width of the wires (5) ofthe first plurality and alternately being in electrical contact with theupper and lower sides of corresponding photovoltaic elements (3) andbeing isolated from the other surface.
 18. A PV cell or a PV modulecomprising at least one electrode (16) or one electrode (16) accordingto any of the preceding claims, comprising one or more photovoltaiccells (3) with an electrically conductive, antireflective, opticallytransparent coating (4) on at least one of its surfaces, the wires (5′)of the first plurality being soldered onto the coating (4) and onto therespective terminal bars (20) or terminal frames (17) by means of thealloy (2).
 19. A PV cell or a PV module according to claim 18 comprisingan electrode (16) according to claim 2, wherein the wires (5′, 5″) ofthe first and second pluralities are bonded together at their crossingpoints and onto the respective terminal bars or terminal frames by meansof the alloy (2).